Amiloride-Sensitive Na+ Transport Mechanisms

Benos, Dale J.; Warnock, David G.; Smith, Jeffrey B.

doi:10.1007/978-3-642-76983-2_4

Cited by 6 publications

(4 citation statements)

References 311 publications

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“…A likely explanation of the above observations is that, since transferrin has a lower affinity for manganese than for iron (Tan & Woodworth, 1969;Scheuhammer & Cherian, 1985), some manganese, but not iron, can dissociate from transferrin in the extracellular medium or after binding to membrane receptors and can be taken up as ionic Mn2+, a process which is facilitated by extracellular KCI but inhibited by NaCl. When receptors for transferrin are (Morgan, 1988; (Jan & Chien, 1973;Cafiso, McLaughlin, McLaughlin & Winiski, 1989;Singh, Kasinath & Lewis, 1992 The inhibition produced by amiloride and NaCl suggests that Mn2+ transport is competing with a Na+ transport process since amiloride is known to inhibit many such processes (Benos, Warnock & Smith, 1992 port, the sensitivity of low affinity Mn2+ transport to the various inhibitors examined in this investigation is very similar to that of the antiport (Flatman, 1991;Gunther, 1993). Hence, one may conclude that Mn2+ can be transported into rabbit erythroid cells by the same mechanism.…”

Section: Mna+ Uptake From Nacl Solutionsupporting

confidence: 55%

“…The different effects of NaCl and KCl, and the greater sensitivity to inhibition by MgCl2 than by CaCl2, are other distinguishing features. The inhibition produced by amiloride and NaCl suggests that Mn2+ transport is competing with a Na+ transport process since amiloride is known to inhibit many such processes (Benos, Warnock & Smith, 1992). This effect plus inhibition by MgCl2, imipramine and quinidine, suggest that the Mn2+ is transported by the Na+-Mg2+ antiport, which normally functions to transport Mg2+ out of erythrocytes in exchange for extracellular Na+.…”

Section: U8mentioning

confidence: 99%

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Mechanisms of manganese transport in rabbit erythroid cells.

Chua

Stonell

Savigni

et al. 1996

The Journal of Physiology

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1. The mechanisms of manganese transport into erythroid cells were investigated using rabbit reticulocytes and mature erythrocytes and 54Mn‐labelled MnCl2 and Mn2‐transferrin. In some experiments iron uptake was also studied. 2. Three saturable manganese transport mechanisms were identified, two for Mn2+ (high and low affinity processes) and one for transferrin‐bound manganese (Mn‐Tf). 3. High affinity Mn2+ transport occurred in reticulocytes but not erythrocytes, was active only in low ionic strength media such as isotonic sucrose and had a Km of 0.4 microM. It was inhibited by metabolic inhibitors and several metal ions. 4. Low affinity Mn2+ transport occurred in erythrocytes as well as in reticulocytes and had Km values of approximately 20 and 50 microM for the two types of cells, respectively. The rate of Mn2+ transport was maximal in isotonic KCl, RbCl or CsCl, and was inhibited by NaCl and by amiloride, valinomycin, diethylstilboestrol and other ion transport inhibitors. The direction of Mn2+ transport was reversible, resulting in Mn2+ efflux from the cells. 5. The uptake of transferrin‐bound manganese occurred only with reticulocytes and depended on receptor‐mediated endocytosis of Mn‐Tf. 6. The characteristics of the three saturable manganese transport mechanisms were similar to corresponding mechanisms of iron uptake by erythroid cells, suggesting that the two metals are transported by the same mechanisms. 7. It is proposed that high affinity manganese transport is a surface representation of the process responsible for the transport of manganese across the endosomal membrane after its release from transferrin. Low affinity transport probably occurs by the previously described Na(+)‐Mg2+ antiport, and may function in the regulation of intracellular manganese concentration by exporting manganese from the cells.

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Section: Mna+ Uptake From Nacl Solutionsupporting

confidence: 55%

Section: U8mentioning

confidence: 99%

Mechanisms of manganese transport in rabbit erythroid cells.

Chua

Stonell

Savigni

et al. 1996

The Journal of Physiology

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“…A reduction in the external [Na + ] from 137 to 50 mM resulted in a reduction in apparent K i , consistent with competitive antagonism of the effect of amiloride by Na + . Amiloride has additional inhibitory effects on the Na + −H + exchanger, on the Na + –Ca 2+ exchanger and on Na + –coupled solute transport (Benos, 1988; Benos et al 1992; Barbry & Hofman, 1997). However, it is not yet known whether these are expressed in human endometrial epithelial cells, while apparent K i values differ significantly between epithelial Na + channels and these other amiloride‐sensitive transport mechanisms.…”

Section: Discussionmentioning

confidence: 99%

Absorptive apical amiloride‐sensitive Na⁺ conductance in human endometrial epithelium

Matthews

McEwan

Redfern

et al. 1998

The Journal of Physiology

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Human endometrial epithelial cells cultured on porous tissue culture supports formed tight, polarized epithelial monolayers with features characteristic of tight epithelia. Endometrial epithelial layers generated significant transepithelial electrical resistance (750 Ω cm2) and potential difference (15.3 mV), with an inward short‐circuit current (Isc; 20.5 μA cm−2). The Isc was linearly proportional to the external Na+ concentration and was abolished in the absence of Na+. The Isc was sensitive to apical amiloride. Net 22Na+ flux was in the absorptive apical to basolateral direction and fully accounted for the inward Isc. In addition, apical to basolateral and net 22Na+ transport were reduced in the presence of amiloride. The Isc was also sensitive to addition of ouabain and Ba2+ to the basal solution, consistent with a role for basolateral Na+−K+‐ATPase and K+ channels in generation of the current. These data demonstrate that human endometrial epithelial cells in primary culture produce tight, functional monolayers on permeable supports. We provide the first evidence that human endometrial epithelial cells have an inward Isc accounted for by an amiloride‐sensitive Na+ conductance. The Na+‐absorptive function of the endometrium may provide an appropriate environment for sperm function and embryo growth.

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“…The Na+-Ca 2+ exchange mechanism makes a prominent contribution to Ca 2+ regulation in heart and brain, as well as certain vascular smooth muscle cells (Benos, Warnock & Smith, 1991). Gmaj, Murer and Kinne (1979) demonstrated Na+-Ca 2+ exchange activity in basolateral membranes from rat renal cortex.…”

Section: Introductionmentioning

confidence: 98%

Sodium-calcium exchange in renal epithelial cells: Dependence on cell sodium and competitive inhibition by magnesium

Lyu

Smith

1991

J. Membrain Biol.

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Kinetic properties of Na(+)-Ca2+ exchange in a renal epithelial cell line (LLC-MK2) were assessed by measuring cytosolic free Ca2+ with fura-2 and 45Ca2+ influx. Replacing external Na+ with K+ produced relatively small increases in free Ca2+ and 45Ca2+ uptake unless the cells were incubated with ouabain. Ouabain markedly increased cell Na+ and strongly potentiated the effect of replacing external Na+ with K+ on free Ca2+ and 45Ca2+ uptake. 45Ca2+ influx in 140 mM K+ or N-methyl-D-glucamine minus influx in 140 mM Na+ was used to quantify Na(+)-Ca2+ exchange activity of Na(+)-loaded cells. The dependence of exchange on cell Na+ was sigmoidal; the K0.5 was 26 +/- 3 mmol/liter cell water space, and the Hill coefficient was 3.1 +/- 0.2. The kinetic features of the dependence of exchange on cell Na+ partly account for the small increase in Ca2+ influx when all external Na+ is replaced by K+. Besides raising cell Na+ ouabain appears to activate the exchanger. Magnesium competitively inhibited exchange activity. The potency of Mg2+ was 8.2-fold lower with potassium instead of N-methyl-D-glucamine or choline as the replacement for external Na+. Potassium also increased the Vmax of exchange by 86% and had no effect on the Km for Ca2+. The exchanger does not cause detectable 22Na(+)-Mg2+ exchange and does not appear to require K+ or transport 86Rb+. Although exchange activity was plentiful in the epithelial cells from monkey kidney, others from amphibian, canine, opossum, and porcine kidney had no detectable exchange activity. All of the measured kinetic properties of Na(+)-Ca2+ exchange in the renal epithelial cells are very similar to those of the exchanger in rat aortic myocytes.

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Amiloride-Sensitive Na+ Transport Mechanisms

Cited by 6 publications

References 311 publications

Mechanisms of manganese transport in rabbit erythroid cells.

Mechanisms of manganese transport in rabbit erythroid cells.

Absorptive apical amiloride‐sensitive Na⁺ conductance in human endometrial epithelium

Sodium-calcium exchange in renal epithelial cells: Dependence on cell sodium and competitive inhibition by magnesium

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Amiloride-Sensitive Na+ Transport Mechanisms

Cited by 6 publications

References 311 publications

Mechanisms of manganese transport in rabbit erythroid cells.

Mechanisms of manganese transport in rabbit erythroid cells.

Absorptive apical amiloride‐sensitive Na+ conductance in human endometrial epithelium

Sodium-calcium exchange in renal epithelial cells: Dependence on cell sodium and competitive inhibition by magnesium

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Absorptive apical amiloride‐sensitive Na⁺ conductance in human endometrial epithelium